1. Field of the Invention
The present invention relates to an aqueous inkjet recording ink and a method for producing the same.
2. Description of the Related Art
As a colorant used in an inkjet recording ink, a pigment is widely used from the view point of resistance to light or resistance to water and the like. For a case in which a pigment is dispersed and used, various studies have been carried out to develop techniques for improving dispersion particle diameter, stability after dispersion, uniformity of dispersion size and the like.
For example, a dispersion method using a surfactant in an emulsified composition state in which a solvent, a polymer and a pigment form a discontinuous phase has been disclosed (for example, see U.S. Pat. No. 4,665,107). According to this method, water forms a continuous phase, and an aqueous dispersion is obtained by removing the solvent after the dispersion step. In addition, a method has been disclosed which comprises adding an aqueous phase comprising a surfactant to a dispersion comprising a polymer, a solvent and a pigment, and removing the solvent to obtain an aqueous dispersion (for example, see European Patent No. 0274961).
Meanwhile, as a method for producing microcapsules, a method has been disclosed in which without using a surfactant, submicron capsules having a gloss developing property are formed by using a self-dispersing resin which can be self-dispersed in a mean particle diameter of 0.1 μm or less under an action of an aqueous medium (for example, see Japanese Patent Application Laid-Open (JP-A) No. 3-221137 and JP Patent No. 3301082).
However, according to the conventional methods which use a surfactant as described above, fine particles cannot be obtained which is required for inkjet ink, and also, due to the use of a surfactant, an unnecessary surfactant is introduced into the ink. In terms of ejection stability, it is preferable that a surfactant is not included in inkjet ink.
In addition, in the method in which a self-dispersing resin is used, there are problems that the particle diameter for inkjet ink, and the dispersion stability of the ink which comprises a water-soluble organic solvent is insufficient.